The reason this show is so good

It's about family values. The police stuff obviously is a big part of the show, but even in that, there is a huge amount of integrity, honesty, justice and righteousness shown.

The Reagan family is a beautiful family and conduct themselves in a very proper manner. They are humans afterall, and err now and then, and towards each other, but they make it right, and also in a proper manner.

This show sets a high standard on morality of the characters and that's why it's so easy to come back to.